Power amplifier circuit



May 27, 1952 E. T. BURTON POWER AMPLIFIER CIRCUIT Filed Nov. 8, 1947 Il l INPUT e (non AMP. 23V) 2 SHEETS-SHEET 1 L I l /m/wron E. 7'. BURTON ATTORNEY M43' 27, 1952 E. 1'. BURTON 2,598,221

A POWER AMPLIFIER CIRCUIT Filed Nov. e, 1947 2 mrs- SHEET 2 WAVE PPL/E0 T0 'YM/DING 2l 0F MOTOR MM/mmm Anm/mn MAM/mnh UUUUUUUUUUUUUIUUUUUUUUUUUUUU WAVE APPL/E0 7D WIND/NG f 0F MGTOR VOLT/46E ronaus T/ME N0 INPUT HAVE WITH INPUT WAVE A WWTI'I INPUT WAVE l F/G 4 TUBE V/ A-G- 5 PLATE CIRCUIT PLATE CIRCUIT SIGNAL WAVE s/cNAL mw: ms s/As f l r/Mf: /A/I/ENTOR By ETBURTON A TTORNEV Patented May 27, .1952

POWER AMPLIFIER CIRCUIT Everett T. Burton, Millburn, N. J., assigner to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York ApplioationfNovember 8, 1947, Serial No. 784,885

4 Claims. 1

rEhis invention relates to circuit arrangements utilizing unilaterally conducting devices -of the type commonly used as amplifiers, and more specifically to arrangements using a pair of such devices to which are applied in both the input and the output circuits thereof voltages of varie able intensity.

A principal object of the invention is to amplify signals in a very eiiicient mannery from the power output standpoint.

It is still another object of this invention to utilize unfiltered, full-wave rectified, alternating current in a power amplier -which is suitable, by Way of example, for a follow-up circuit, that is, a circuit for causing one shaft to follow the rotation of another shaft located at a distant point, and more specifically for a follow-up circuit utilizing a two-phase alternating current motor. Such a follow-up circuit can be utilized, by way of example, in a radar system having a rotary element associated with a yrange dial if it is desired to cause a rotary element at a distant station, or at another point at the same station too remote for direct'connection to the first rotary element, to follow the rotation of the first rotary element. The second rotary element can be used to impart Yacornponent of motion to a computer or director or to an optical sight or range nder. In such a follow-up circuit, the signal applied to the amplifier is an alternating Wave of a fixed frequency but which varies between two phaseconditions 180 degrees apart with respect to a reference wave.

In a copending application of E. T. Burton, Serial No. 491,789, led June 22', 1943, and which issued on January 13, 1948, as. Patent 2,434,259, there is disclosed a four-tube amplifier used in a follow-up arrangement in which one shaft Vis adapted toA rotate in accordance with the rotation of another shaft ata point too distant` to malte a mechanical connection practical. The four-tube amplifier can be considered as two groups of two tubes each. One pair ofthe two pairs of tubes operates (in alternate half cycles). when the inputsignal wave has Vone of its two phase conditions and the other pair operates (in alternate half cycles) when the input Wave has the other of its two phase conditionswith respect to the reference Wave. The four-tube arrangement has an `alternating voltage rwave applied to the anode-cathodeV circuit of each tube and an alternating grid' biasing vvoltage Kwave applied to each cathode-grid` circuit,r thegrid` bias wave in each tube being of the same frequency and displaced 180 degrees from the plate circuitv volt-age wave thereof. The present invention is a modiiication of the four-tube arrangement shown in the copending Burton application and, as it utilizes a fewer number of tubes, may be more suitable in some installations thanthe four-tube arrangement.

in accordance with the present invention, there is provided a power amplifier circuit utilizing two tubes. Unltered, full-wave rectified, alternating voltage is applied between the anode and cathode of each tube and a similar vwave but of opposite phaser and smaller amplitude is applied between the control element and cathode of each tube, whereby in the absence of signal waves both tubes are cut ofi. If an alternating signal, either in phase with or 180 degrees out of phase-with the wave` rectiiied to produce the anode voltage, is applied in push-pull manner to the input circuits of the two? tubes,` the two tubesccnduct alternately, each for a half cycle. The amplifier is very eilicient from the power output standpoint because each tube is conducting for only a fraction of the time and the voltage on the control element is maximum when the plate voltage is also a maximum.v The instantaneous Ymaximum power output from each tube can therefore far exceed the ratedpower output of the tube.

The invention will be more readily understood by referring to the following description taken in connection with the accompanying drawings forming a part thereof, in which:

Eig. 1 is a block diagram of a follow-up system utilizing a power amplifier in accordance with the invention;

Fig. 2 is a circuit diagram of a portion of the apparatus oi Fig. l including the two-tube'amplier arrangementin accordance with the invention; and

Figs. 3 and 4 are various graphical and diagrammatical vrepresentations to aid in understanding the invention.

Referring more specically to the drawings, Fig. l shows, by way of example to illustrate the principles ci the invention, a follow-upisystem which is used to reproduce at a remote station, or at a distant point at the same station, bythe rotation of a secondshaft, the rotation of'a first rotatable shaft. The first shaft can be, for example, that driving the range dial in a distance indicatingsystem of thev pulse reflection. type or a shaft driven thereby or therewith. This first rotatable shaft is represented as the angular out-v put device IB in Fig. 1 and is geared or otherwise mechanically connected to the rotor II of the sending Selsyn I2 which has a stator member i3 provided with a distributed poly-circuit winding which may be similar to the usual threephase winding of an alternating current dynamo-electric machine. The winding may be either Y- or delta-connected. The single circuit rotor winding II is connected by means of the conductors I4 and I5 to a source of alternating current I6. The stator I3 is connected by means of the conductors I1, I3 and I9, which can be of considerable length, to the stator of the receiving Selsyn 2|, which has a rotor member 22 provided with a single circuit winding. The receiving Selsyn 2I is in all respects similar to the transmitting Selsyn I2 but the rotor Winding 22 of the receiving Selsyn is connected to the input circuit of the amplifier 23 instead of to the alternating source I6. The term Selsyn is being used in the broad sense to include all devices of the general character of the members I2 and 2 I.

At this point the operation of the sending and receiving Selsyns I2 and 2I will be explained. The rotor Winding II of the sending Selsyn I2, when energized with current from the alternating current source I6, produces an alternating magnetic eld by means of which a voltage is induced in the stator winding I3, thereby causing current to fiow in the stator winding 23 of the receiving Selsyn 2I. These currents in the stator winding 20 produce an alternating magnetic field by means of which a voltage is induced in the rotor winding 22, when the relationship between the axis of the rotor winding and the axis of the magnetic field is other than 90 degrees. When this E-degree relationship obtains, no voltage is induced in the rotor winding and, consequently, no component voltage is applied to the input circuit of the amplifier 23 with the result that the system is deenergized and at rest, However, when the rotor Il of the sending Selsyn is rotated, a magnetic field is set up which induces a voltage in the rotor winding 22 which is either in phase with the voltage wave from the alternating source I6 (which latter wave will hereinafter be designated the reference wave (see Fig. 3A) or have a phase relationship 180 degrees with respect thereto. This voltage induced in the rotor winding 22 is insumcient to produce a torque large enough to turn the armature of the Selsyn 2I (particularly if a load 30 such as a computer or optical range finder is applied thereto). The amplier 23, which is of any suitable form, the power amplier 24 (including the rectiiiers therefor) and the followup motor 26 serve as a torque amplifier for the receiving Selsyn 2I. The voltage output of the amplifier 23 is applied to the power amplier 24 which preferably comprises the two-tube arrangement shown in Fig. 2 and which will be described in detail below. The device 24 produces an amplified version of the output wave of the amplifier 23. The output wave of the amplifier 24 is either in phase with the reference wave from the source I6 or 180 degrees out of phase with respect thereto. This output wave is applied to the eld winding 25 of the follow-up motor 26, the other field winding 21 of which is connected through a QO-degree phase shifter 28 to the alternating current source I6. The motor 26 has an armature 29 which is geared or otherwise mechanically connected to drive the rotary member 22 in such a direction that the voltage in the input circuit of the amplifier 23 is reduced to zero. The load 30, which may be a computer or optical range finder or any other mechanical device which it is desired to have follow the motion of the device I0, is geared or otherwise mechanically connected to the armature 29 of the motor 26 o1' to the armature 22 of the receiving Selsyn 2|. The follow-up motor 26 can be of any suitable two-phase type, preferably one which has a low inertia. Such a motor operates by having two alternating voltages applied to its two field windings, these voltages being substantially 90 degrees apart in phase. It will be appreciated that as the voltage applied to the winding 21 (see Fig. 3B) is 90 degrees out of phase with respect to the reference potential from the alternating current source I6, and as the winding 25 has applied thereto a voltage wave (see Fig. 3C) which may be at one particular time in phase with the voltage wave from the alternating current source I6 and at another particular time 180 degrees out of phase with respect to the reference wave from the source I6 (the particular condition depending on which direction the rotary armature II of the sending Selsyn I2 is driven and hence the direction that the induced voltage of rotary member 22 takes), then the phase of the voltage wave applied to the winding 25 is either plus or minus 90 degrees with respect to the voltage wave applied to the winding 21, as indicated in Fig. 3C. Thus the armature 29 of the motor 26 will be actuated in one direction or the other to reduce to zero the voltage applied to the input of the amplifier 23, at which time the position of the rotor 22 of the receiving Selsyn 2| will correspond with the position of the rotor of the sending Selsyn I2.

Reference will now be made to Fig. 2 which is a circuit diagram of a portion of the apparatus shown within dot-dash lines in Fig. 1. The circuit arrangement of Fig. 2 includes a first tube VI and a second tube V2. These tubes can be of any suitable type but are preferably high vacuum tubes. Tube VI comprises an anode 40, a cathode 4I, a control grid 42, a screen grid 43 and a suppressor grid 44. Tube V2 has corresponding elements to 54, inclusive. Each of the suppressor grids is connected to a corresponding cathode. 'I'he cathodes 4I and 5I are connected together and their common terminal is connected to ground which is one output terminal of three rectifiers 56, 51 and 58 each of which receives Sil-cycle alternating current power from a source 59 and produces a full-wave, unfiltered output. Any suitable full-wave unfiltered rectiners may be used as members 56, 51 and 58, the specic details of these rectiflers being no part of this invention. These rectifiers must bear phase interrelationship of zero or 180 degrees as will be described below. These phase differences are also i90 degrees with respect to the input to motor winding 21 in Fig. 1. Each rectifier has in its input circuit a transformer having a turn ratio such that the rectifier 56 produces an output voltage of the order of 50 volts, the rectifier 51 an output voltage of about 400 volts, and the rectifier 58 an output voltage of about 1350 volts. The ungrounded terminal 60 of the rectier 56 is negative with respect to ground while the corresponding terminals 6I and 52 of the rectifiers 51 and 58, respectively, are positive with respect to ground.

The plate or anode voltage for tubes VI and V2 is supplied by the rectifier 58, the terminal 62 being connected to the mid-terminal 63 of the primary winding 64 of a transformer 65, the seccathodes.

-ondary winding -66 of which is connected to the output circuit. vThe-two outer terminals-'f the Winding 64 are connected, respectively, to the anodesfll and `l) of the tubes VI- and" V2, respectively. -Since the other terminal of rectier 58 ample, volts peak, is applied between the common cathode connectionand mid-tap 61 of the secondary Winding 68 of the input transformer 69, the primary windingv 10 ofwhich is connected to the amplifier 23. The .outside terminals Yof the secondary winding 68 Vare applied, 'respectively, tothe control grids'42 and-52 of the tubes VI and V2. respectively. To "produce proper phasing, the resistor 1I and the capacitor12are connected in a series circuit which is shunted across the upper half of the secondary Winding 68 and resistor I3 and capacitor 14 are connected in a series circuit which is shunted across the lower part of this winding.

The screen grids i3 and153 are connected together and their common terminal is connected to the output terminal El ofthe rectifierE'! which delivers a full-wave rectied vuniiltered output voltage of about 400 volts positive with respect to ground. rIhis wave is of the same frequency and in phase with the wave applied in theanode circuit of each of rthe tubes VI4 and V2.

The signal or input wave applied to the input transformer winding 'Hi from the amplifier 23 can have any value from zero to a'peak of 50 volts or even somewhat higher if the. grids 42 and 52 are to be drivenpositive with respect to their This signal valve is of theV same form as that shown in Fig. 3C andis amplied subl stantially without distortion by the power amplifier 24 before beingapplied to the winding 25.

The use of alternating voltage which has'been rectified and left unfiltered results in a considerable improvement from the standpoint of tube power loss since thelimit of power output is in part dependent on the heat dissipating capabilities of the tube elements involved. By varying the plate and screen voltages between zero and four-tube circuit shown in the-above-identied Burton patent, but in the present invention fewer tubes are required to produce a result which is almost as eihcient from the-power output 'standpoint. At the same time it does the same work as the four-tube arrangement shown in the Burton patent, since in the present arrangement one of the tubes in the pair is operating at all times regardless of the phase of the input signal, whereas in the earlier arrangement described in the Burton patent, one pair of two tubes operates (in alternate half cycles) when the input signal wave has one of the two phase conditions, and the other .pair operates (in alternate half cycles) when the input Wave has the other ofitsitwo phase conditions with respect tothe reference The operation of the arrangement shown in Figs. 1 and 2 will now be described. Ylli" the kshaft of the motor member I0 is turned, a rotation of the rotary armature Il of the sending Selsyn l2 is produced which, in the manner pointed out above, causes a voltage to be induced in the armaturev 22 of the receiving Selsyn 2|. vThe Voltage induced in the Winding 22 may be, for example, of the form shown in Fig. 3C, the notation +96 degrees indicating that this portion of the wave 'leads by 90 degrees the wave shown in Fig. 3B

(which is the Wave applied to the Winding 21 of the motor 26) and the notation -90 degrees indicating that thisfportion of the wave is lagging the wave shown in Fig. 3B by 90 degrees. The wave shown in Fig.`3B is displaced 90 degrees with respect to the reference wave shown in Fig. 3A, the wave produced by the source I6. 'Ihe torque of the motor 26 for a signal wave of the type shown in Fig. 3C is indicated in'Fig. 3D. It Will be noted that it is in one direction (positive) for certain periods, and in an opposite direction (negative) for` other periods, these periods being determined by the direction of rotation of the shaft of the motor Ill and hence by the sign of the voltage-induced in the winding22.

The operation of the two-tube amplifier arrangement 24 will be more readily appreciated by considering the various curves shown in. Fig. 4. Fig. 4A1 shows in full lines the plate circuit voltage curve for the tube VI and in dash lines the grid bi-as voltage of the same tube. The same two curves are shown in Fig. 4B1 for the tube V2. It will be noted that in the absence of a signal Wave, the grid voltage wave is maintained degrees out of phase with the plate circuit Voltage wave so that no current flows in either of the tubes when no input wave lappears in the primary windingr 'lll of the input transformer 69. ANow assume that the. input wave in the primary winding 10 (for atleast a cycle of the Wave shown in Fig. 3C) has'one of its two possible phase conditions, which' one condition is called Input wave A and is so designated at the top of the second column of the various diagrams collectively designated Fig. 4. Because of lthemanner ofl connection of the transformer winding 68, the-input wave applied to the' control grid of the tube Vl is `180 degrees out of phase with respect to the wave applied to the control grid 52 of the tube V2. In

Figs. 4A2 and `fiBZ the plate circuit voltage` and the input voltage wave have been shown in full lines, the grid bias wavehasbeenshownA in dash llines and the algebraic sum of the input wave and the. grid bias wave h-as also been shown-in dash lines. These curves are for the tubes VI` and V2 respectively. As indicated in these figures, the input signal wave is of somewhatlarger magnitude than the grid bias Wave, although it will be appreciated that this is not always necessary. Obviously, the magnitude of the plate circuit voltage Wave ismuch larger in relation to that of the signal or grid bias wave than has been indicated in the drawings. In the con-dition shown in the second column of Fig. 4, this being indicated 1nput wave A, tube Vl conducts current during the first half cycle of signal Wave input because both the control grid and the anode of this tube are positive. During this half wave, tube V2 does not conduct current because although the plate voltage is positive, the signal Wave is negative during this half cycle. In the second half cycle of the input wave A, the tube Vl is not conducting because the signal voltage wave is negative, but the tube V2 is conducting because both the plate circuit voltage wave and the signal wave are positive, Now if the input wave in the primary winding has the second of these two conditions, which condition will be called Input wave B and is so designated at the top of the third column of the diagram comprising Fig. 4, it will be appreciated from a study of Figs. 4A3 and 4B3 that during the rst half cycle tube V2 conducts and Vl does not, while in the second half cycle tube Vl conducts and tube V2 does not.

It should be noted that the output waves are ampliiied replicas of the input waves A and B due to the fact that the output currents of the tubes Vl and V2 iiow in opposite directions through the transformer winding 64. These amplied waves are applied to the winding 25 of the motor 26 and produce torque in one direction or the other to drive the rotor member 22 in a direction to reduce the voltage induced in the winding 22 to zero, as indicated in the middle portion of the curve of Fig. 3C. The computer or optical range finder 30 is also driven by the motor 26 (or by the rotor member 22) through a gear train or other suitable mechanical means so that a shaft or other movable member therein tends to follow the movement of the rotary member in the motor I0. As examples of suitable computers (directors) utilizing range information imparted as a rotary movement, reference is made to the book "Elements of Ordnance" by Hayes, chapter XIV.

Various modiiications can be made in the circuit arrangement described above without departing from the spirit of the invention the scope of which is indicated in the claims. In the claims,

vthe term signal is intended to apply to waves of the kind utilized in electrica1 control systems, electric power systems, etc. as well as the kind employed strictly for conveying intelligence.

What is claimed is:

1. In combination, two discharge devices in push-pull relationship, each comprising an anode, a cathode and a control element, means for applying a iirst rectified sine full-wave which varies from zero to maximum during each half cycle of the sine wave between the cathode and anode of each of said devices, and means including means for applying a similar rectified sine fullwave in opposite phase with respect to the rst full-wave between the cathode and the control element of each device for keeping the anode current in each device in the vicinity of anodecurrent cutoii during the full-wave cycle.

2. In combination, two discharge devices in push-pull relationship, each comprising a cathode, an anode and a control element, means for rectifying a iirst alternating voltage sine wave and deriving therefrom a rectiiied full-wave which varies from zero to maximum during each half cycle of the sine wave, means for applying said rectied full-wave between the cathode and anode of each device, means for applying a similar rectified full-wave in opposite phase thereto between the cathode and control element of each device, and means for applying as a signal voltage an alternating voltage sine wave of the frequency of said iirst sine wave and at a phase difference of mr therewith (where 'n is zero or any integer between the cathode and control element of each device.

3. In combination, two discharge devices in push-pull relationship, each comprising a cathode, an anode and a control element, means for rectifying a rst alternating voltage sine wave and deriving therefrom a rectified full wave which varies from zero to maximum during each half cycle of the sine wave, means for applying said rectified full-wave as anode voltage between the cathode and anode of each device, means including means for applying a similar rectified fullwave at opposite phase with respect to said rstmentioned rectiiied full-wave as a biasing voltage between the cathode and control element of each device for keeping the anode current in each device in the vicinity of anode-current cutoff during the full-wave cycle, and means for applying as a signal voltage an alternating voltage sine wave of the frequency of the first sine wave at a phase difference of mr therewith (where n is zero or any integer) between the cathode and anode of each device for causing anode current to iiow in only one of said devices.

4. In combination, two discharge devices in push-pull relationship, each comprising a cathode, an anode, a screen grid and a control element, means for rectifying a first alternating voltage sine wave and deriving therefrom a rectied full-wave which varies from zero to maximum during each half cycle of the sine wave, means for applying said rectified full-wave to each device between the cathode and anode and between the cathode and screen grid, means for applying a similar rectified full-wave in opposite phase with respect to said rst full-wave between the cathode and control element of each device, and means for applying as a signal voltage an alternating voltage sine wave of the frequency of said iirst sine wave and at a phase difference of n1.- therewith (where n is zero or any integer) between the cathode and control element of each device.

EVERETT T. BURTON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,669,958 Walsh May 15, 1928 1,752,839 Gardiner Apr. 1, 1930 1,892,924 Babler Jan. 3, 1933 1,940,723 Miessner Dec. 26, 1933 2,070,772 Ansley Feb. 16, 1937 2,226,746 Schulze-Herringen Dec. 3l, 1940 2,273,150 Shepard Feb. 17, 1942 2,352,103 Jones June 20, 1944 2,393,936 Romander Jan. 29, 1946 

